Middle Pennsylvanian (Desmoinesian) Fusulinids of the Bug Scuffle Limestone Member of the Gobbler Formation, Sacramento Mountains, South-Central New Mexico

Abstract

Analysis of fusulinids from the Bug Scuffle Limestone Member of the Gobbler Formation along the western escarpment of the Sacramento Mountains in south-central New Mexico demonstrates that all four Desmoinesian regional fusulinid zones documented in Midcontinent and Southwest North America are present in the stratigraphic unit. Earliest Desmoinesian (Df1 Zone) fusulinids from the basal Bug Scuffle limestone beds suggest that the carbonate unit transgressed northward on the Sacramento Shelf, with Beedeina insolita in basal beds of the southernmost canyon exposures, and the slightly more advanced B. hayensis and B. curta in basal limestone beds of more northern outcrops. Late early Desmoinesian (Df2 Zone) fusulinids are common and widespread throughout the escarpment outcrop belt indicating that it was the time period with the most widespread normal marine shelf paleoenvironmental conditions. The diverse assemblage of the Df2 Zone is characterized by Beedeina novamexicana, B. euryteines, B. leei, B. socorroensis, B. joyitaensis, Wedekindellina euthysepta, and W. excentrica. The microprobematical branching fossil Komia is also common in this zone. Wedekindellina and Komia do not range above the mid-Desmoinesian CSB1 composite sequence boundary. Above that sequence boundary, the early late Desmoinesian Df3 Zone is characterized by sparse Beedeina haworthi, and the closely related B. illinoisensis and B. tumida. The late late Desmoinesian Df4 Zone is represented by a diverse assemblage of fusulinids in the uppermost part of the Bug Scuffle Limestone Member in the southern canyon exposures, including Beedeina acme, B. megista, B. mysticensis, B. lonsdalenesis, B. bellatula, B. gordonensis, and B. vintonensis. No Beedeina identifiable to species were found in upper part of the Bug Scuffle Limestone Member in the northernmost canyon exposures, demonstrating that late Desmoinesian paleoenvironments became more restricted marine northward along the Sacramento Shelf. Above the CSB2 composite sequence boundary in the uppermost Bug Scuffle Limestone Member, the lower part of the uppermost depositional sequence continues to contain latest Desmoinesian Df4 Zone fusulinids in the southern canyon sections. Early Missourian conodonts have been reported in a limestone unit near the top of the Gobbler clastic detrital member in the north-central part of the outcrop belt(Wahlman and Barrick 2018; Lucas et al. 2021), but no early Missourian conodonts or fusulinids have been reported yet from the uppermost Bug Scuffle Limestone Member in the southern canyons.